1. Field of the Invention
The present invention relates to a keypad assembly and more particularly to a keypad having a light guide panel and a keypad assembly.
2. Description of the Related Art
FIG. 1 is a sectional view of a first exemplary keypad assembly according to the prior art. The keypad assembly 100 includes a keypad 110, a switch board 150, and a plurality of light emitting diodes (LEDs) 170.
The keypad 110 includes an elastic pad 120, a plurality of key buttons 140 having characters, symbols, letter, etc., formed on their upper surface and lying on the upper surface 122 of the elastic pad 120, and a plurality of protrusions 130 formed on the lower surface 124 of the elastic pad 120. Respective key buttons 140 are aligned with corresponding protrusions 130 and switches 160 in the transverse direction of the keypad assembly 100. The elastic pad 120 has a plurality of grooves 126 formed on its lower surface 124 around respective protrusions 130 to prevent the LEDs 170 and the protrusions 130 from interfering with each other.
The switch board 150 has a printed circuit board (PCB) 155 and a plurality of switches 160 formed on the upper surface of the PCB 155, which faces the keypad 110. Each switch 160 consists of a conductive contact member 162 and a conductive dome 164 completely covering the contact member 162.
The LEDs 170 are mounted on the upper surface of the PCB 155 and are positioned in such a manner that they are covered with corresponding grooves 126 of the elastic pad 120.
If the user presses one of the key buttons 140, a portion of the keypad 110 lying beneath the pressed key button 140 is deformed towards the switch board 150. As a result, a protrusion 130 belonging to the deformed portion compresses the corresponding dome 164, which then makes an electric contact with the corresponding contact member 162.
FIG. 2 is a sectional view of a second exemplary keypad assembly according to the prior art. The keypad assembly 200 includes a keypad 210, an electroluminescence sheet 260, a switch board 250, and a driving unit 280.
The keypad 210 includes an elastic pad 220, a plurality of key buttons 230 having characters, etc. formed on their upper surface, and lying on the upper surface of the elastic pad 220, and a plurality of protrusions 240 formed on the lower surface of the elastic pad 220. Respective key buttons 230 are aligned with corresponding protrusions 240 and switches 270 in the transverse direction of the keypad assembly 200.
The switch board 250 has a PCB 255 and a plurality of switches 270 formed on the upper surface of the PCB 255. Each switch 270 consists of a conductive contact member 272 and a conductive dome 274 completely covering the contact member 272.
The electroluminescence sheet 260 is positioned to cover the upper surface of the PCB 255 with the switches 270 interposed between them, and emits light in response to an applied driving signal.
The driving unit 280 is mounted on the upper surface of the PCB 255 while being positioned on one side of the electroluminescence sheet 260, and applies a driving signal to the electroluminescence sheet 260.
However, the above-mentioned keypad assemblies 100 and 200 have the following problems.
In the case of the first exemplary keypad assembly 100, light emitted by respective LEDs 170 passes through the elastic pad 120 and reaches corresponding key buttons 140 at an oblique angle. As a result, illumination of the key buttons 140 is uneven and insufficient. More particularly, the center of each key button 140 appears darker than its periphery. However, use of more LEDs for even and sufficient illumination of the key buttons 140 makes the construction complicated and increases the power consumption and manufacturing cost.
The second exemplary keypad assembly 200 provides much less sufficient illumination than the first example.
Therefore, it is requested to provide a keypad assembly providing even and sufficient illumination, consuming less power, and having simple construction.